Conventional cover windows of touch panels are usually made of reinforced glass but lack flexibility and thus are inapplicable to flexible products. In view of this, it is important to develop a cover window which substitutes for conventional glass-based cover windows and has flexibility and satisfactory optical and physical properties, for example, regarding rigidity.
Taiwan patent 1457635 discloses a retardation film which has a uniform Re (in-plane retardation) and is made of monopropylene resin with an isotactic index of above 85%. The retardation film is capable of insignificant zero wavelength dispersion and displays high uniformity of Re (in-plane retardation) values at a specific point, with a mean deviation of ±5 nm. The retardation film capable of insignificant zero wavelength dispersion and the other retardation films capable of negative wavelength dispersion are stacked to manufacture a stacked optical film capable of positive wavelength dispersion.
However, the penetrating ray of Taiwan patent 1457635 is not uniformly distributed on a visible region and thus does not address the aforesaid issues: optical rainbow patterns and visibility under a polarizer.
Referring to FIG. 1, since the coating layer and the substrate do not match in terms of the refractive index, the incident ray ends up with reflected ray 1 and reflected ray 2 which have a phase difference therebetween. The reflected rays 1, 2 which have a phase difference therebetween produce rainbow patterns when observed by users with the naked eye.
Hence, related apparatus manufacturers and researchers look forward to developing a plastic cover window which substitutes for conventional glass cover windows, has flexibility features and surface rigidity, reduces rainbow patterns, and enhances visibility under a polarizer.